This invention relates to a concrete filled tube column and a method of constructing the same, the concrete filled tube column constituting, for example, a part of a building structure, such as a column and a pile.
FIGS. 1 to 3 show an example of a conventional concrete filled tube column constituting a part of a building structure. This column 20 is made of a steel outer tube 22 within which concrete is filled to form a concrete core 24. The outer tube 22 includes a plurality of tube bodies 26, and a plurality of joint tubes 28. Each joint tube 28 coaxially interconnects two adjoining tube bodies 26. The beams 30 of the building structure are welded to the outer face of each joint tube 28 so that an axial load is transmitted from the beams 30 to the outer tube 22. Furthermore, a pair of vertically spaced parallel inner flanges 32 are circumferentially welded on the inner face of each joint tube 28, and project radially inward into the concrete core 24 to transmit the axial load from the outer tube 22 to the core 24. In this column, the axial compressive strength of the concrete core 24 is enhanced by the lateral confinement of the outer tube 22, and thereby it is possible to considerably reduce the cross-sectional area of the column in comparison with the cross-sectional area of a conventional concrete column without an outer tube.
However, upon the construction of the above-described column, there arises an inconvenience that air spaces and rock pockets tend to be generated in the concrete core 24 because of the inner flanges 32. For example, when concrete is charged into an erected outer tube 22 to form the concrete core 24, the inner flanges 32 become obstacles to air smoothly flowing upward and discharging from the outer tube 22, resulting in the air spaces 34 (see FIG. 3) confined between the charged concrete and the lower surfaces of the inner flanges 32. In addition to the above example, during the curing of the charged concrete, the inner flanges 32 also become obstacles to the setting of the concrete, i.e., the downward movement of the concrete due to the contraction of the concrete. This fact also results in the air spaces 34 generated under the inner flanges 32. These air spaces 34 not only prevent the inner flanges 32 from transmitting the axial load from the outer tube 22 to the core 24 but also reduce the axial compressive strength of the concrete core 24. Furthermore, upon the setting of the concrete, since the concrete paste contained in the concrete flows downward more smoothly than the aggregates contained in the concrete, the aggregates tend to gather around the inner flanges 32 and form the rock pockets 36 (see FIG. 3) in the concrete core 24. These rock pockets 36 also reduces the axial compressive strength of the concrete core 24.
In order to avoid the generation of the air spaces and the rock pockets, the charging of the concrete may be stopped every time the concrete is filled in the outer tube 22 up to the level of one of the inner flanges 32. After the charged concrete is hardened, concrete charging may be resumed until the concrete is filled up to the next inner flange 32. However, such a process of concrete charging considerably lengthen the construction period of the column 20.